Chapter 9 new

Mader: Biology 8th Ed.

The Cell Cycle and Cellular Reproduction

Chapter 9


Interphase

• Most of the cell cycle is spent in interphase.– G1 - Cell doubles its organelles and

accumulates materials needed for DNA synthesis.

– S - DNA replication.– G2 - Cell synthesizes proteins necessary

for cell division.


Mitotic Stage

• Cell division stage that includes mitosis (nuclear division or karyokinesis) and cytokinesis (cytoplasm division).


Cell Cycle

GO


Cell Cycle Control

• Regulated by external signals (e.g., growth factors) and internal signals

• Researchers have identified internal signal protein (cyclin) that increases and decreases as cell cycle continues.


Cell Cycle Control

• Cyclins– Must be present for the cell to proceed

from the G2 stage to the M stage and from G1 stage to S stage.

Allows time for any damage to be repaired.


Cell Cycle Control

Signaling protein p53; stop to repair damage OR apoptosis


Apoptosis

• Programmed cell death (or cell suicide)– Normal part of development

– Protects against cancer

9 week embryo

froglet


Apoptosis

– Cells have enzymes (caspases) necessary for apoptosis to occur.

Ordinarily held in check by inhibitors, but can be unleashed by internal or external signals.

• Mitosis increases and apoptosis decreases the number of somatic cells.


Apoptosis


Chromosomes

• When a eukaryotic cell is

not undergoing division,

the DNA within the

nucleus is a tangled

mass of chromatin.– DNA wraps around

histones– Condenses into chromosomes

(6 ft of DNA in each human cell)


Chromosomes

• Each species has a characteristic number of chromosomes.– Diploid (2n) -

Two of each kind.

– Haploid (1n) - One of each kind.


Mitosis

• During mitosis, a diploid nucleus divides to produce diploid daughter nuclei.– Two identical chromatids are called sister

chromatids.Attached to each other at centromere.

During nuclear division, sister chromatids separate at the centromeres, and each duplicated chromosome gives rise to two daughter chromosomes.


Duplicated Chromosomes

Each chromosome as it passes through cell cycle…

G1 phase S phase End of mitosis

one copy of info DNA replicated; Sister chromatids separate;2 copies of info Each cell has 1 copy of info

Centromere

1 sister chromatid


Mitosis in Animal Cells

• Each centrosome in an animal cell contains a pair of barrel-shaped organelles (centrioles) and an array of short microtubules (aster).

– http://www.biostudio.com/d_%20Mitosis.htm

http://www.biostudio.com/d_%20Mitosis.htm



• Prophase– Chromatin has condensed.– Nucleolus disappears.– Nuclear envelope disintegrates.– Spindle begins to assemble.

• Prometaphase– Kinetochores develop on centromere.

Attach sister chromatids to spindle fibers.




• Metaphase– Chromosomes, attached to kinetochore

fibers, are in alignment at center of cell.• Anaphase

– Sister chromatids split, producing daughter chromosomes.

Daughter chromosomes are pulled to opposite poles.



• Telophase– Spindle disappears as new nuclear

envelopes form around the daughter chromosomes.

Chromosomes become diffuse chromatin again.

Nucleolus appears in each daughter nucleus.



Cytokinesis

• Cytokinesis accompanies mitosis in most cells, but not all.– Mitosis without cytokinesis results in a

multinucleated cell.Begins in anaphase, continues in

telophase, but does not reach completion until the following interphase begins.


Cytokinesis

• Animal Cells– Cleavage furrow, membrane indentation

between daughter nuclei, begins as anaphase nears completion.

Deepens when a band of actin filaments (contractile ring) forms a circular constriction between the two daughter cells.


Cytokinesis in Animal Cells


Plant Cell Division

• Meristematic plant tissue retains the ability to divide throughout the plant’s life.– Found at root and shoot tips.


Phases of Mitosis in Plant Cells


Cytokinesis

• Plant Cells– Rigid cell wall of plant

cells does not permit cytokinesis by furrowing.

Begins with formation of a cell plate which eventually becomes new plasma membrane between the daughter cells.


The Cell Cycle and Cancer

• Cancer is a growth disorder that results from the mutation of genes regulating the cell cycle.– Carcinogenesis, development of cancer,

tends to be gradual.



Characteristics of Cancer Cells

• Lack differentiation.• Have abnormal nuclei.• Form tumors.

– Loss of contact inhibition.• Undergo metastasis.

– New tumors distant from primary tumor.• Undergo angiogenesis.

– Formation of new blood vessels.



Origin of Cancer

• Mutations in DNA repair mechanisms.• Mutations to proto-oncogenes.

– Proto-oncogenes become oncogenes.• Mutations to tumor-suppressor genes.

– Includes p53• Telomerase allows cancer cells to

continually divide.– Telomere = tip of chromosome that is

shortened with each cell division– Telomerase MAINTAINS telomeres


Prokaryotic Cell Division

• Asexual Reproduction - offspring are genetically identical to the parent.– Binary fission produces two (binary)

daughter cells that are identical to the original parent.

Prokaryotes contain a single chromosome with only a few proteins.

(E. coli has about 4,000 genes. Humans have about 25,000 genes.)


Binary Fission

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Chapter 9 new